A known form of burner assembly has a head assembled within a refractory block forming part of a furnace wall. Fuel gas is supplied to the head and the flow of gas inspirates air to mix with the fuel gas prior to discharge from jets in the head. The air and fuel gas mixture is passed through a venturi prior to discharge. It is generally desirable to ensure that the combustion process yield low level of nitrogen-oxides (NOx) pollutants and a general object of the present invention is to provide an improved burner assembly of the aforementioned kind in which NOx emission is minimised.